Displays may receive information from a central processor or sensor, and translate the information in a manner that a viewer prefers. In certain cases, the displays are digital or analog, or a combination of both.
One such widely implemented display is a pointer. A pointer is often driven by a motor in a manner to rotate from a first position to a second. The motor is electrically driven by a certain predefined amount, with the rotation corresponding to a specific value or indicia. Thus, when the tip of the pointer points at a specific value, the pointer is indicating a current or recent state associated with a machine.
Pointers driven by motors are commonly implemented in vehicles. A pointer device receives information from a vehicle sensor, for example, a speed sensor, a fuel sensor, an engine sensor, or the like—and translates the received information into a specific value to point at.
Different motors have been implemented for this application. One such motor is the stepper motor. The stepper motor is a brushless direct current (DC) electric motor that divides a full rotation into a number of equal steps.
Various implementations of stepper motors have been realized, based on the operation and other aspects. One such implementation is a stepper motor that uses a microstep. The microstep is defined as a stepper motor that employ microstepping (or “sine cosine microstepping”). The microstepping may employ a sinusoidal alternating current (AC) waveform. One justification for employing microstepping is that a finer resolution of step size may be achieved. Thus, a full rotation may provide more distinct step positions versus other type of stepper motors.
In order to calibrate a microstep motor, an offset is determined. Knowing the offset allows for a more accurate implementation of the motor. Each microstep motor may have an individual offset caused by variations in the motor properties, such as magnets, materials, and other factors. Thus, if a specific microstep motor's offset is known, the operation or driving of the microstep motor may be adjusted based on the known offset for a more accurate and calibrated performance.
FIG. 1(a) shows a stepper motor 10 according to the prior art. As shown, the stepper motor 10 includes a first conductive core 12, a second conductive core 14, first inductive coil 16, a second inductive coil 18, and a permanent magnet 20. It is understood that the stepper motor 10 may include any number of conductive cores and coil windings, as desired.
The first conductive core 12 may be formed from any conductive material such as metal, for example. The first conductive core 12 is disposed adjacent the permanent magnet 20, wherein the permanent magnet 20 is free to rotate. As shown, the first conductive core 12 includes a first conductive core aperture 22, the permanent magnet 20 disposed therein. Although the first conductive core 12 is shown having a rectangular shape, it is understood that the first conductive core 12 may have any shape and size, as desired.
The second conductive core 14 may be formed from any conductive material such as metal, for example. The second conductive core 14 is disposed adjacent the permanent magnet 20, wherein the permanent magnet 20 is free to rotate. As shown, the second conductive core 14 includes a second conductive core aperture 24, the permanent magnet 20 disposed therein. Although the second conductive core 14 is shown having a rectangular shape, it is understood that the second conductive core 14 may have any shape and size, as desired.
The first inductive coil 16 may be formed from any conductive material such as metal, for example. The first inductive coil 16 includes a first inductive coil first lead 26 and a first inductive coil second lead 28. Each lead 26, 28 is adapted for electrical communication with a source of electrical energy (not shown). The first inductive coil 16 is wound around at least a portion of the first conductive core 12. It is understood that the first inductive coil 16 may have any number of turns or windings.
The second inductive coil 18 may be formed from any conductive material such as metal, for example. The second inductive coil 18 includes a second inductive coil first lead 30 and a second inductive coil second lead 32. Each lead 30, 32 is adapted for electrical communication with a source of electrical energy. The second inductive coil 18 is wound around at least a portion of the second conductive core 14. It is understood that the second inductive coil 18 may have any number of turns or windings.
The permanent magnet 20, also referred to as a magnetic rotor, is shown as a magnetic disk having a first magnetic pole 34 and a second magnetic pole 36. It is understood that the permanent magnet 20 may have any shape, as desired. It is further understood that the permanent magnet 20 may have any number or orientation of magnet poles, as desired. The permanent magnet 20 is disposed adjacent the first conductive core 12 and the second conductive core 14. The permanent magnetic 20 further includes a rotor shaft 38 having an axis 37, the rotor shaft 38 adapted to control the rotational motion of a secondary device such as an instrument pointer, for example.
FIG. 1(b) shows a programmable control system 40 in electrical communication with a stepper motor 10 according to a prior art implementation. The programmable control system 40 includes a plurality of programmable control system inputs 42, a control unit 44, and a detector device 46.
The plurality of programmable control system inputs 42 is adapted to receive an electrical signal such as a sinusoidal or triangular voltage waveform, for example. As shown, the programmable control system inputs 42 are in electrical communication with the stepper motor 10. Although the programmable control system 40 is shown having four programmable control system inputs 42, it is understood that the programmable control system 40 may have any number of programmable control system inputs 42, as desired.
The control unit 44 includes a drive circuit 48, a rectification device 50, and an integrator device 52. The drive circuit 48 is in electrical communication with the plurality of electrical leads 26, 28, 30, 32 of the stepper motor 10. The drive circuit 48 is adapted to provide an electric current to the stepper motor 10. It is understood that the drive circuit 48 may provide electrical communication between the electrical leads 26, 28, 30, 32 of the stepper motor 10 and the source of electrical energy. The rectification device 50 is in electrical communication with the programmable control system inputs 42. The rectification system 50 may be any conventional system for rectifying an electric signal and providing an output signal having a single polarity such as multiplexer circuitry, for example. The integrator device 52 is in electrical communication with the rectification device 50 and the detector device 46. It is understood that the integrator device 52 may be any conventional device, wherein an output signal 53 of the integrator device 52 is proportional to the integral of an input signal of the integrator device 52 such as an operation amplifier integrator, for example.
The detector device 46 includes a detector input 54 and a detector output 56. It is understood that the detector device 46 may be any conventional device for receiving an electrical signal, measuring the electrical signal, and transmitting an output relating to the signal measurement such as a microcomputer, for example. The detector device 46 may further include a programmable function, wherein the function provides measurement and analysis of characteristics of the stepper motor 10 such as rotational velocity and accumulated back EMF, for example. The detector input 54 is in electrical communication with the integrator device 52 of the control unit 44. The detector output 56 is in electrical communication with a feedback loop 58. The detector output 56 is adapted to transmit an output signal 57 of the detector device 46 to the feedback loop 58. As shown, the feedback loop 58 is in electrical communication with the control unit 44, specifically, the drive circuit 48. It is understood that the output signal 57 of the detector device 46 may be transmitted to the drive circuit 48, wherein the output signal 57 is received by the drive circuit 48 to control the rotation of the stepper motor 10. It is further understood that the output signal 57 of the detector device 46 may be transmitted to a display device (not shown), wherein a user may analyze and interpret the output signal 57.
In operation, the drive circuit 48 provides an effective voltage across the first inductive coil 16, wherein the voltage causes an electric current to flow through the first inductive coil 16. As the change in electric current occurs, a magnetic field is induced within the first inductive coil 16. The magnetic field is channeled through the first conductive core 12 toward the permanent magnet 20. When the magnetic field from the first inductive core 16 and the magnetic field from the permanent magnet 20 are not aligned, the permanent magnet 20 will rotate about the axis 37 of the rotor shaft 38. Because opposite magnetic fields attract and like fields repel each other, this rotation continues until the magnetic fields of the permanent magnet 20 have aligned with the opposite pair of magnetic fields from the first inductive coil 16. After the permanent magnet 20 has rotated into the new position, it settles and stops moving. It is understood that to keep the permanent magnet 20 rotating, the magnetic field from both the first inductive coil 16 and the second inductive coil 18 must be changed periodically in a sequence with alternating magnetic fields that keep the permanent magnet 20 in an unstable state and rotating in a desired direction.
Conventionally, microstep motor offsets are determined by experimental or observational techniques. Thus, during production, a microstep motor offset may be viewed or observed, with the offset being recorded by the viewer. However, this technique may not be accurate and/or efficient.